844 research outputs found
Spin squeezing and precision probing with light and samples of atoms in the gaussian approximation
We consider an ensemble of trapped atoms interacting with a continuous wave
laser field. For sufficiently polarized atoms and for a polarized light field,
we may approximate the non-classical components of the collective spin angular
momentum operator for the atoms and the Stokes vectors of the field by
effective position and momentum variables for which we assume a gaussian state.
Within this approximation, we present a theory for the squeezing of the atomic
spin by polarization rotation measurements on the probe light. We derive
analytical expressions for the squeezing with and without inclusion of the
noise effects introduced by atomic decay and by photon absorption. The theory
is readily adapted to the case of inhomogeneous light-atom coupling [A. Kuzmich
and T.A.B. Kennedy, Phys. Rev. Lett. Vol. 92, 030407 (2004)]. As a special
case, we show how to formulate the theory for an optically thick sample by
slicing the gas into pieces each having only small photon absorption
probability. Our analysis of a realistic probing and measurement scheme shows
that it is the maximally squeezed component of the atomic gas that determines
the accuracy of the measurement.Comment: 12 pages, 5 figure
Magnetometry with entangled atomic samples
We present a theory for the estimation of a scalar or a vector magnetic field
by its influence on an ensemble of trapped spin polarized atoms. The atoms
interact off-resonantly with a continuous laser field, and the measurement of
the polarization rotation of the probe light, induced by the dispersive
atom-light coupling, leads to spin-squeezing of the atomic sample which enables
an estimate of the magnetic field which is more precise than that expected from
standard counting statistics. For polarized light and polarized atoms, a
description of the non-classical components of the collective spin angular
momentum for the atoms and the collective Stokes vectors of the light-field in
terms of effective gaussian position and momentum variables is practically
exact. The gaussian formalism describes the dynamics of the system very
effectively and accounts explicitly for the back-action on the atoms due to
measurement and for the estimate of the magnetic field. Multi-component
magnetic fields are estimated by the measurement of suitably chosen atomic
observables and precision and efficiency is gained by dividing the atomic gas
in two or more samples which are entangled by the dispersive atom-light
interaction.Comment: 8 pages, 11 figure
Combined state and parameter estimation for on-line applications,
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 1972.Bibliography: leaves 354-361.by Peter S. Maybeck.Ph.D
Large array of GFETs for extracellular communication with neuronal cells
Graphene has already shown its high ability for biosensing. Solution-gated graphene field effect transistors, which showed very high sensitivity in electrolytes [1], have another biologically important application: recording neuronal activity. Such devices exhibit very high signal-to-noise ratio for extracellular measurements [2]. The aim of this work is to optimize and scale both fabrication procedure and measurement system. When working with biological samples, there is a need in a large number of devices. High density of the devices is also preferable. Therefore we fabricate the devices on 4ââ wafer, resulting in 50 chips, 11*11mm each. Each chip consequently embodies an array of 32 graphene FETs (see fig.1). The active area of the chip is around 2 mm2 while each GFETâs channel differs between 5 and 20 um with altered configurations. Such devices, when used with the already developed multichannel measurements system make possible simultaneous measurement and stimulation of all 32 transistors in a time-scale. This makes possible to measure not just discrete spikes, but even propagation of the action potential through the neuronal network
Errors in quantum optimal control and strategy for the search of easily implementable control pulses
We introduce a new approach to assess the error of control problems we aim to
optimize. The method offers a strategy to define new control pulses that are
not necessarily optimal but still able to yield an error not larger than some
fixed a priori threshold, and therefore provide control pulses that might be
more amenable for an experimental implementation. The formalism is applied to
an exactly solvable model and to the Landau-Zener model, whose optimal control
problem is solvable only numerically. The presented method is of importance for
applications where a high degree of controllability of the dynamics of quantum
systems is required.Comment: 13 pages, 3 figure
Implementation Lessons and Pitfalls for Real-time Optimal Control with Stochastic Systems
Modern computational power and efficient direct collocation techniques are decreasing the solution time required for the optimal control problem, making real-time optimal control (RTOC) feasible for modern systems. Current trends in the literature indicate that many authors are applying RTOC with a recursive open-loop structure, relying on a high recursion rate for implicit state feedback to counter disturbances and other unmodeled effects without explicit closed-loop control. The limitations of using rapid, instantaneous optimal solutions are demonstrated analytically and through application to a surface-to-air missile avoidance control system. Two methods are proposed for control structure implementation when using RTOC to take advantage of error integration through either classical feedback or disturbance estimation
AUV SLAM and experiments using a mechanical scanning forward-looking sonar
Navigation technology is one of the most important challenges in the applications of autonomous underwater vehicles (AUVs) which navigate in the complex undersea environment. The ability of localizing a robot and accurately mapping its surroundings simultaneously, namely the simultaneous localization and mapping (SLAM) problem, is a key prerequisite of truly autonomous robots. In this paper, a modified-FastSLAM algorithm is proposed and used in the navigation for our C-Ranger research platform, an open-frame AUV. A mechanical scanning imaging sonar is chosen as the active sensor for the AUV. The modified-FastSLAM implements the update relying on the on-board sensors of C-Ranger. On the other hand, the algorithm employs the data association which combines the single particle maximum likelihood method with modified negative evidence method, and uses the rank-based resampling to overcome the particle depletion problem. In order to verify the feasibility of the proposed methods, both simulation experiments and sea trials for C-Ranger are conducted. The experimental results show the modified-FastSLAM employed for the navigation of the C-Ranger AUV is much more effective and accurate compared with the traditional methods
Nonlinear Semi-Analytic Methods for Trajectory Estimation
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/76298/1/AIAA-29106-621.pd
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